1. Field of the Invention
The present invention relates to the technology of transmitting/receiving a traffic indication message in a wireless communication system.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating the construction of a typical wideband wireless communication system. Respective MS (Mobile Stations) 10 and 12 generally have mobility, and are connected to a backbone network 30 through respective BSs (Base Stations) 20 and 22. The MS 10 and 12 provide connections between the BSs 20 and 22 and subscribers (not shown). Additionally, the BSs 20 and 22 provide functions for controlling, and managing MS 10 and 12 and for connectivity of the MS 10 and 12. The backbone network 30 is connected to an ASA (Authentication and Service Authorization Server) 40 for the authentication of the MS 10 and 12 and service authorization.
Reducing power consumption is an important factor for MS supporting mobility. One method for reducing the power consumption of the MS is to employ a sleep mode. In the sleep mode, all functions (e.g., transmission functions, reception functions, etc.,) of the MS other than for an RTC (Real Time Clock) function and a PLL (Phase Locked Loop) function, are stopped. During the sleep mode, the PLL remains in an active state so that the MS can be easily awakened (i.e., returned to a normal state), thus ending the sleep mode. While in the sleep mode, the MS is periodically awakened in order to perform a search, a ranging, or a handover for neighboring BS's, etc. A wideband wireless communication system which functions under standard such as the Institute for Electrical and Electronics Engineers (IEEE) 802.16E, standard (the Standard), reduces the power consumption of the MS and allows the MS to perform a handover more smoothly when in the sleep mode.
Specifically, the MS that enters into the sleep mode undergoes a sleep interval and a listening interval. For a frame corresponding to the sleep interval, the MS stops the transmission/reception of data to reduce its power consumption, and for a frame corresponding to the listening interval, the MS may, depending upon the situation, return to a normal state to perform a periodic ranging. In other words, the MS that enters into the listening interval should be awakened because the MS should decode a TRF-IND (Traffic Indication) message transferred from the BS and determine whether there is any DL (Download) traffic, for the MS and may also take advantage of a periodic ranging opportunity. That is, the MS should return to a receiving state by awakening from the sleep mode and returning to a normal state (i.e., an awake state).
The corresponding BS should transmit the traffic indication to the MS that is in a sleep mode and that is managed by the BS itself at the listening interval using a broadcast CID. Accordingly, the BS, if it receives incoming data of a specified MS that is operating in a sleep mode, may buffer the corresponding traffic data until the corresponding MS reaches its listening interval. The BS may drop the incoming data according to the existing conditions. Hereinafter, the procedure of performing the sleep mode by the MS will be explained with reference to FIG. 2.
FIG. 2 is a flow diagram illustrating a procedure of performing a sleep mode by an MS. The MS 10 transmits a request message MOB-SLP-REQ to the BS 20 so that it can enter into the sleep mode at step 50. The BS 20 that has received the request message transmits a response message MOB-SLP-RSP for informing the corresponding MS 10 of an approval/rejection of the request so that the corresponding MS 10 can enter into the sleep mode at step 52. The MS 10, if it receives the response message from the BS 20, enters into the sleep mode. As described above, the MS 10 undergoes the sleep interval 60 and the listening interval 62 in the sleep mode.
Then, the BS 20 sends the MS 10 a traffic indication message MOD-TRF-IND for informing the MS of the existence of a corresponding MS-related message and traffic data buffered in the BS 20 to match the listening interval 62 of the corresponding MS 10 according to a sleep mode pattern agreed through the request/response messages. If the traffic indication message is received, the MS 10 checks if the MS-related message and the traffic data exist in the traffic indication message, and if so, MS 10 shifts to an awake state in which the MS 10 can receive the message.
Here, the traffic indication message MOB-TRF-IND is a type of broadcasting message that indicates the existence or nonexistence of traffic of a plurality of MS. Specifically, the BS broadcasts the traffic indication message that indicates the existence or nonexistence of traffic to the plurality of MS that share the listening interval. However, according to the present standard, the BS cannot properly provide the traffic indication message to the MS that is in the sleep mode.
In other words, due to a vague definition, in the Standard as described above, the BS cannot transfer a functional traffic indication message to the MS that are in the sleep mode through the MOB-TRF-IND message.